// geohash.js
// Geohash library for Javascript
// (c) 2008 David Troy
// Distributed under the MIT License

BITS = [16, 8, 4, 2, 1];

BASE32 = "0123456789bcdefghjkmnpqrstuvwxyz";
NEIGHBORS = { right  : { even :  "bc01fg45238967deuvhjyznpkmstqrwx" },
    left   : { even :  "238967debc01fg45kmstqrwxuvhjyznp" },
    top    : { even :  "p0r21436x8zb9dcf5h7kjnmqesgutwvy" },
    bottom : { even :  "14365h7k9dcfesgujnmqp0r2twvyx8zb" } };
BORDERS   = { right  : { even : "bcfguvyz" },
    left   : { even : "0145hjnp" },
    top    : { even : "prxz" },
    bottom : { even : "028b" } };

NEIGHBORS.bottom.odd = NEIGHBORS.left.even;
NEIGHBORS.top.odd = NEIGHBORS.right.even;
NEIGHBORS.left.odd = NEIGHBORS.bottom.even;
NEIGHBORS.right.odd = NEIGHBORS.top.even;

BORDERS.bottom.odd = BORDERS.left.even;
BORDERS.top.odd = BORDERS.right.even;
BORDERS.left.odd = BORDERS.bottom.even;
BORDERS.right.odd = BORDERS.top.even;

function refine_interval(interval, cd, mask) {
    if (cd&mask)
        interval[0] = (interval[0] + interval[1])/2;
  else
        interval[1] = (interval[0] + interval[1])/2;
}

function calculateAdjacent(srcHash, dir) {
    srcHash = srcHash.toLowerCase();
    var lastChr = srcHash.charAt(srcHash.length-1);
    var type = (srcHash.length % 2) ? 'odd' : 'even';
    var base = srcHash.substring(0,srcHash.length-1);
    if (BORDERS[dir][type].indexOf(lastChr)!=-1)
        base = calculateAdjacent(base, dir);
    return base + BASE32[NEIGHBORS[dir][type].indexOf(lastChr)];
}

function decodeGeoHash(geohash) {
    var is_even = 1;
    var lat = []; var lon = [];
    lat[0] = -90.0;  lat[1] = 90.0;
    lon[0] = -180.0; lon[1] = 180.0;
    lat_err = 90.0;  lon_err = 180.0;

    for (i=0; i<geohash.length; i++) {
        c = geohash[i];
        cd = BASE32.indexOf(c);
        for (j=0; j<5; j++) {
            mask = BITS[j];
            if (is_even) {
                lon_err /= 2;
                refine_interval(lon, cd, mask);
            } else {
                lat_err /= 2;
                refine_interval(lat, cd, mask);
            }
            is_even = !is_even;
        }
    }
    lat[2] = (lat[0] + lat[1])/2;
    lon[2] = (lon[0] + lon[1])/2;

    return { latitude: lat, longitude: lon};
}

function encodeGeoHash(latitude, longitude) {
    var is_even=1;
    var i=0;
    var lat = []; var lon = [];
    var bit=0;
    var ch=0;
    var precision = 12;
    geohash = "";

    lat[0] = -90.0;  lat[1] = 90.0;
    lon[0] = -180.0; lon[1] = 180.0;

    while (geohash.length < precision) {
      if (is_even) {
            mid = (lon[0] + lon[1]) / 2;
        if (longitude > mid) {
                ch |= BITS[bit];
                lon[0] = mid;
        } else
                lon[1] = mid;
      } else {
            mid = (lat[0] + lat[1]) / 2;
        if (latitude > mid) {
                ch |= BITS[bit];
                lat[0] = mid;
        } else
                lat[1] = mid;
      }

        is_even = !is_even;
      if (bit < 4)
            bit++;
      else {
            geohash += BASE32[ch];
            bit = 0;
            ch = 0;
      }
    }
    return geohash;
}